Our progress in the last year is summarized below: 1. Novel adult stem cell sources - We have reported on the discovery and characterization of multipotent mesenchymal progenitor cells from new human tissue sources: (1) palatine tonsils, (2) dental pulp, (3) umbilical cord;and (4) traumatized muscle. These cells exhibit multiple differentiation potential (osteo-, chondro-, and adipogenesis), express surface epitope characteristic of MSCs, and are immunosuppressive in a mixed lymphocyte reaction. We have examined the molecular signature of these MSCs from different tissue sources to gain insight into how their cell fate and differentiation may be differentially regulated. 2. Wnt signaling mechanisms in MSCs - Both canonical (involving beta-catenin) and non-canonical Wnt signaling mechanisms operate in the MSCs in vitro, involving multiple Frizzled and LRP receptors. The former appears to act to enhance self-renewal and proliferation and suppress differentiation, whereas the latter appears to act to enhance or stabilize lineage-specific differentiation induced by specific growth factors and culture conditions. The involvement of Wnt signaling is likely to be critical in regulating the cell fate of MSCs. 3. Differentiation and maturation of MSCs - We have initiated a study on the tenogenic differentiation of MSCs as a model to understand tendon development and repair. In addition, we have characterized the regulation of chondrocytic hypertrophy in chondrifying pellet cultures of MSCs, for the purpose of developing means to regulate this undesirable premature development of MSCs in cell-based approaches to cartilage regeneration. 4. "Stemness" genes and "Reprogramming" genes - In a previous study based on differential gene expression analyses, we have identified candidate genes that may function to maintain MSCs in an undifferentiated, self-renewal ready state. A number of genes, including those encoding intracellular signaling and cytoskeletal proteins, extracellular matrix components (e.g., laminin alpha 4, and cytokines (e.g., IL-6) are being analyzed for their cellular and molecular mechanisms of action. In addition, the action of the 4 reprogramming genes, first reported by the Yamanaka group, is also being examined in terms of self-renewal and differentiation activities. Results from these studies should shed significant light on the basic mechanisms regulating stem cell activity as well as on potential approaches to direct their activities for applications in cell-based therapy.